Preparation of sunlight-driven lignin-based interface evaporator

Abstract

The invention discloses a preparation method of a sunlight-driven lignin-based interface evaporator, which comprises the following steps: firstly, improving the light absorption and photo-thermal conversion performance of lignin by doping metal ions, then preparing a photo-thermal material and a polyvinyl alcohol solution into a prepolymerization solution, and finally, forming photo-thermal hydrogel under the crosslinking of glutaraldehyde. Compared with existing lignin, the light absorption and photo-thermal conversion performance of the lignin can be greatly improved through simple metal ion doping, and therefore it is ensured that the lignin can be subjected to seawater desalination with high efficiency.

Description

Technical Field

[0001] The present invention relates to the fields of lignin functional materials and seawater desalination, and particularly to the design of lignin photothermal materials and interfacial evaporation devices. Background Art

[0002] With the growth of social economy and the continuous increase of the global population, the shortage of water resources and energy crisis have become obstacles that cannot be ignored. The rich water resources in the ocean have attracted much research interest in obtaining fresh water through seawater desalination. However, current seawater desalination methods such as membrane separation technology and thermal distillation usually have defects such as high cost, high energy consumption, and secondary pollution, which limit the popularization of these seawater desalination methods in underdeveloped areas.

[0003] Solar interfacial evaporation technology is a new seawater desalination method that uses photothermal materials to capture solar energy and convert it into heat energy, and evaporates brine at the evaporation interface to obtain fresh water. As the most important part of solar interfacial evaporation, photothermal materials can be divided into four categories: plasma metal materials (such as gold and silver), semiconductor materials (such as TiO x , CuS, etc.), carbon materials (such as carbon nanotubes, graphene, and carbon black), and polymer materials (such as dopamine, polypyrrole, and polyaniline). However, traditional photothermal materials generally have problems such as cumbersome preparation processes, high energy consumption, and high costs. Different from the need for high-cost and complex synthesis steps, natural materials such as dopamine and tannic acid also show excellent potential for solar interfacial evaporation.

[0004] However, lignin, as the second largest biomass resource after cellulose, has not been applied to interfacial photothermal evaporation technology because of its low light absorption and photothermal conversion performance. Based on this problem, the present invention proposes to improve the light absorption and photothermal conversion performance of lignin by doping metal ions. Through the coordination between metal ions and the phenolic hydroxyl groups of lignin, the optical band gap (the energy level difference between the ground state and the excited state) of lignin materials is reduced to enhance the light absorption range and photothermal performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for enhancing the light absorption and photothermal conversion performance of lignin, so as to solve the two problems of narrow light absorption range and poor photothermal conversion of existing lignin, and thus apply lignin to solar interfacial evaporation.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A preparation method of a sunlight-driven lignin-based photothermal hydrogel. First, the light absorption and photothermal conversion performance of lignin are enhanced by doping with metal ions. Then, a photothermal material and a polyvinyl alcohol solution are prepared into a prepolymer solution. Finally, a photothermal hydrogel is formed under the crosslinking of glutaraldehyde. The specific steps are as follows:

[0008] (1) Preparation of the photothermal material: Dissolve lignin and an iron compound in deionized water at a mass ratio of 10:1 - 1:5 to obtain an aqueous solution of an iron ion-doped lignin photothermal material.

[0009] (2) Preparation of the polyvinyl alcohol solution: Dissolve polyvinyl alcohol solid in deionized water to obtain an aqueous solution of polyvinyl alcohol. (3) Preparation of the hydrogel prepolymer solution: Add the solution of the lignin photothermal material obtained in step (1) to the polyvinyl alcohol solution in step (2) and mix evenly to obtain a mixed solution; the mass concentration of polyvinyl alcohol in the mixed solution is 5% - 10%, and the mass concentration of iron ion-doped lignin is 0.1% - 10%.

[0010] (4) Preparation of the photothermal hydrogel: Use an acid to adjust the pH value of the mixed solution obtained in step (3) to 1 - 6, add a glutaraldehyde solution and mix evenly. Then, pour the hydrogel prepolymer solution into a mold and initiate a crosslinking reaction in an oven to obtain the photothermal hydrogel.

[0011] In the present invention, in step (1), the lignin includes at least one of lignin sulfonate (LS), alkali lignin (AL), and demethylated lignin (DML).

[0012] In the present invention, in step (1), the iron compound includes at least one of ferric chloride and its hydrates, ferric sulfate, and ferrous sulfate.

[0013] In the present invention, in step (1), the mass ratio of the lignin to the iron compound is 5:1 - 2:1.

[0014] In the present invention, in step (1), the mixing time of the lignin and the iron compound is 1 - 6 hours, preferably 1 - 2 hours; the temperature is 10 - 80 °C, preferably 20 - 40 °C.

[0015] In the present invention, in step (1), the mass concentration of the lignin in deionized water is 0.1% - 15%.

[0016] In the present invention, in step (1), fully mix polyvinyl alcohol solid and deionized water, and stir and dissolve at 80 - 95 °C for 1 - 6 h to obtain an aqueous solution of polyvinyl alcohol.

[0017] In the present invention, in step (2), the mass concentration of polyvinyl alcohol in the aqueous solution of polyvinyl alcohol is 5%-15%, preferably 7.5%-10%.

[0018] In the present invention, in step (2), polyvinyl alcohol solid and deionized water are fully mixed and stirred and dissolved at 80-95°C for 1-6 h to obtain an aqueous solution of polyvinyl alcohol; the dissolution temperature is preferably 90°C; the stirring time is preferably 3-6 hours.

[0019] In the present invention, in step (3), the concentration of polyvinyl alcohol in the prepolymer solution is 7.5-10%; the concentration of lignin in the prepolymer solution is 1%-5%.

[0020] In the present invention, in step (3), the conditions for uniform mixing are: stirring temperature 20-80°C, preferably 50-80°C, stirring time 0.5-6 hours, preferably 3-6 hours.

[0021] In the present invention, in step (4), the pH value of the mixed solution is 2-5.

[0022] In the present invention, in step (4), hydrochloric acid is used to adjust the pH value of the mixed solution, and the concentration of hydrochloric acid is 0.1-21 M.

[0023] In the present invention, in step (4), the volume concentration of the glutaraldehyde solution is 50%.

[0024] In the present invention, in step (4), the addition amount of the glutaraldehyde solution is 1%-5% of the mass of polyvinyl alcohol. For example, the volume of the glutaraldehyde solution is 0.1-0.5 ml.

[0025] In the present invention, in step (4), the crosslinking temperature is 10-100°C, preferably 60-80°C; the crosslinking time is 1-24 h, preferably 6-12 h.

[0026] The present invention also relates to protecting the sunlight-driven lignin-based photo-thermal hydrogel prepared by the above preparation method.

[0027] A sunlight-driven lignin-based interfacial evaporator, the interfacial photo-thermal evaporator includes an evaporator body, and the evaporator body includes a photo-thermal hydrogel, a water delivery layer, and a heat-insulating foam layer arranged in sequence from top to bottom, and the photo-thermal hydrogel is the above-mentioned sunlight-driven lignin-based photo-thermal hydrogel.

[0028] In the present invention, the water delivery layer is cellulose cotton cloth or dust-free paper, and the heat-insulating foam layer is polystyrene or polyurethane foam.

[0029] In the present invention, the thickness of the photo-thermal hydrogel is 0.5 - 2 cm, the thickness of the water transport layer is 0.01 - 0.5 cm, and the thickness of the heat insulation foam layer is 0.5 - 5 cm.

[0030] In the present invention, it further includes a solar simulator and a data collection system. The solar simulator is used to simulate sunlight irradiation, and the data collection system is used to monitor the performance of the photo-thermal gel.

[0031] In the present invention, the power density of the solar simulator is 0.5 - 5 KW / m 2 .

[0032] The present invention also relates to protecting the application of the above-mentioned solar-driven lignin-based interfacial evaporator in seawater desalination. The seawater can come from the Dalian sea area or can be simulated seawater.

[0033] Beneficial effects: Compared with the existing lignin, the present invention can greatly improve the light absorption and photo-thermal conversion performance of lignin through simple metal ion doping, so as to ensure that lignin can desalinate seawater with higher efficiency. Different from the current mainstream methods for improving the photo-thermal performance of lignin (mainly high-temperature carbonization treatment), the method of the present invention has relatively low energy consumption and mild reaction conditions. At the same time, the present invention illustrates through experimental tests and theoretical calculations that the enhancement of the light absorption and photo-thermal performance of iron ion-doped lignin mainly comes from the change of the energy band structure of lignin. Through solar seawater desalination tests, it is proved that the evaporator prepared by the present invention has a wider range of light absorption and photo-thermal conversion performance, as well as seawater desalination performance. Description of the Drawings

[0034] Figure 1 Transmittance tests of different photo-thermal materials (Example 1, Comparative Examples 1 and 2 correspond to LS-Fe, LS, and Fe in Figure 1 respectively) prepared by the present invention in the wavelength range of 200 - 1100 nm.

[0035] Figure 2 Temperature rise curves of different photo-thermal material powders (the samples obtained by drying in Step 1 of Example 1, Comparative Examples 1 and 2 correspond to LS-Fe powder, LS powder, and FeCl Figure 2 in 3 .6H 2 O) prepared by the present invention under the same light irradiation.

[0036] Figure 3 Band gaps of LS and LS-Fe photo-thermal hydrogels tested by the present invention. Among them, a and b are the Mott-Schottky curves of Comparative Example 1 and Example 1 respectively, c is the test result of VB-XPS, and d is the summary of the tested energy level difference results.

[0037] Figure 4 It is a schematic diagram of the structure of the evaporation device of the present invention.

[0038] Figure 5 Schematic diagram of the cross section of the evaporator.

[0039] Figure 6 The desalination rate of the photothermal water gel prepared in Example 2 of the present invention for salt solutions of different concentrations.

[0040] In the figure: 1. Solar simulator, 2. Evaporator, 3. Electronic balance, 4. Infrared camera, 5. Data recording computer, 6. Photothermal water gel, 7. Insulation foam layer, 8. Water transport layer, 9. Simulated seawater. DETAILED DESCRIPTION

[0041] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0042] Example 1

[0043] A method for preparing a sunlight-driven lignin-based photothermal water gel comprises the following steps:

[0044] (1) Preparation of photothermal material: 10 g of sodium lignin sulfonate (supplier McLean) and 1 g of ferric chloride hexahydrate (supplier McLean) were dissolved in 90 ml of deionized water and mixed thoroughly for 2 h at a reaction temperature of 20 °C to obtain an aqueous solution of iron ion-doped lignin photothermal material (denoted as LS-FE).

[0045] (2) Preparation of polyvinyl alcohol solution: 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water were fully mixed and stirred at 90° C. for 6 h to obtain a polyvinyl alcohol aqueous solution.

[0046] (3) Preparation of hydrogel prepolymer solution: 50 g of the solution of lignin photothermal material obtained in step (1) was added to 100 g of the polyvinyl alcohol solution in step (2). The resulting mixed solution had a polyvinyl alcohol concentration of 10% and an iron ion-doped lignin concentration of 3.3%. Finally, the mixture was stirred at 80° C. for 6 h to obtain a prepolymer solution.

[0047] (4) Preparation of photothermal water gel: The mixed solution obtained in step (3) was adjusted to pH 5 using hydrochloric acid, 0.1 ml of glutaraldehyde (50%) aqueous solution was added and mixed evenly, and then the hydrogel prepolymer was poured into a mold (cylindrical with a diameter of 5 cm and a height of 1 cm), and a cross-linking reaction was initiated in an oven at 60°C for 10 h to obtain a photothermal water gel.

[0048] Example 2

[0049] A preparation method of a sunlight-driven lignin-based photothermal hydrogel, comprising the following steps:

[0050] (1) Preparation of the photothermal material: Dissolve 5 g of sodium lignosulfonate (supplier Macklin) and 1 g of ferric chloride hexahydrate (supplier Macklin) in 45 ml of deionized water, mix well for 2 h, and the reaction temperature is 20 °C to obtain an aqueous solution of a lignin photothermal material doped with iron ions with high photothermal conversion efficiency (denoted as LS-Fe).

[0051] (2) Preparation of the polyvinyl alcohol solution: Thoroughly mix 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water, and stir and dissolve at 90 °C for 6 h to obtain an aqueous solution of polyvinyl alcohol.

[0052] (3) Preparation of the hydrogel prepolymer solution: Take 100 g of the solution of the lignin photothermal material obtained in step (1) and add it to 100 g of the polyvinyl alcohol solution in step (2). In the finally obtained mixed solution, the mass concentration of polyvinyl alcohol is 7.5%, and the mass concentration of iron ion-doped lignin is 5%. Finally, stir at 70 °C for 6 h to obtain the prepolymer solution.

[0053] (4) Preparation of the photothermal hydrogel: Adjust the pH value of the mixed solution obtained in step (3) to 5 with hydrochloric acid, add 0.1 ml of glutaraldehyde (50%) aqueous solution and mix well. Then pour the hydrogel prepolymer solution into a mold (a cylindrical mold with a diameter of 5 cm and a height of 2 cm), and initiate a crosslinking reaction in an oven at 60 °C for 12 h to obtain the photothermal hydrogel.

[0054] Example 3

[0055] A preparation method of a sunlight-driven lignin-based photothermal hydrogel, comprising the following steps:

[0056] (1) Preparation of the photothermal material: Dissolve 2 g of sodium lignosulfonate (supplier Macklin) and 1 g of ferric chloride hexahydrate (supplier Macklin) in 18 ml of deionized water, mix well for 2 h, and the reaction temperature is 20 °C to obtain an aqueous solution of a lignin photothermal material doped with iron ions with high photothermal conversion efficiency (denoted as LS-Fe).

[0057] (2) Preparation of the polyvinyl alcohol solution: Thoroughly mix 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water, and stir and dissolve at 90 °C for 6 h to obtain an aqueous solution of polyvinyl alcohol.

[0058] (3) Preparation of hydrogel prepolymer solution: 50 g of the solution of lignin photothermal material obtained in step (1) was added to 100 g of the polyvinyl alcohol solution in step (2). The resulting mixed solution had a polyvinyl alcohol concentration of 10% and an iron ion-doped lignin concentration of 3.3%. Finally, the mixture was stirred at 80° C. for 6 h to obtain a prepolymer solution.

[0059] (4) Preparation of photothermal water gel: The mixed solution obtained in step (3) was adjusted to pH 5 using hydrochloric acid, 0.1 ml of glutaraldehyde (50%) aqueous solution was added and mixed evenly, and then the hydrogel prepolymer was poured into a mold (cylindrical with a diameter of 5 cm and a height of 1 cm), and a cross-linking reaction was initiated in an oven at 60°C for 10 h to obtain a photothermal water gel.

[0060] Example 4

[0061] A method for preparing a sunlight-driven lignin-based photothermal water gel comprises the following steps:

[0062] (1) Preparation of photothermal material: 4 g of sodium lignin sulfonate (supplier McLean) and 2 g of ferric chloride hexahydrate (supplier McLean) were dissolved in 18 ml of deionized water and mixed thoroughly for 2 h at a reaction temperature of 20 °C to obtain an aqueous solution of iron ion-doped lignin photothermal material with high photothermal conversion efficiency (denoted as LS-Fe).

[0063] (2) Preparation of polyvinyl alcohol solution: 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water were fully mixed and stirred at 90° C. for 6 h to obtain a polyvinyl alcohol aqueous solution.

[0064] (3) Preparation of hydrogel prepolymer solution: 50 g of the solution of lignin photothermal material obtained in step (1) was added to 150 g of the polyvinyl alcohol solution in step (2). The resulting mixed solution had a polyvinyl alcohol concentration of 11% and an iron ion-doped lignin concentration of 5%. Finally, the mixture was stirred at 80° C. for 6 h to obtain a prepolymer solution.

[0065] (4) Preparation of photothermal water gel: The mixed solution obtained in step (3) was adjusted to pH 5 using hydrochloric acid, 0.1 ml of glutaraldehyde (50%) aqueous solution was added and mixed evenly, and then the hydrogel prepolymer was poured into a mold (cylindrical with a diameter of 5 cm and a height of 1 cm), and a cross-linking reaction was initiated in an oven at 60°C for 10 h to obtain a photothermal water gel.

[0066] Example 5

[0067] A method for preparing a sunlight-driven lignin-based photothermal water gel comprises the following steps:

[0068] (1) Preparation of photothermal material: Dissolve 20 g of sodium lignosulfonate (supplier Macklin) and 2 g of ferric chloride hexahydrate (supplier Macklin) in 180 ml of deionized water, mix well for 2 h at a reaction temperature of 20 °C to obtain an aqueous solution of pure lignin photothermal material for comparison (denoted as LS-Fe).

[0069] (2) Preparation of polyvinyl alcohol solution: Thoroughly mix 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water, and stir to dissolve at 90 °C for 6 h to obtain an aqueous solution of polyvinyl alcohol.

[0070] (3) Preparation of hydrogel prepolymer solution: Take 50 g of the solution of lignin photothermal material obtained in step (1) and add it to 100 g of the polyvinyl alcohol solution in step (2). In the finally obtained mixed solution, the mass concentration of polyvinyl alcohol is 10%, and the mass concentration of lignin is 3.3%. Finally, stir at 80 °C for 6 h to obtain the prepolymer solution.

[0071] (4) Preparation of photothermal hydrogel: Adjust the pH value of the mixed solution obtained in step (3) to 5 using hydrochloric acid, add 0.5 ml of glutaraldehyde (50%) solution and mix well. Then pour the hydrogel prepolymer solution into a mold (a cylindrical mold with a diameter of 5 cm and a height of 1 cm), and initiate a crosslinking reaction in an oven at 60 °C for 24 h to obtain the photothermal hydrogel.

[0072] Example 6

[0073] A preparation method of a lignin-based photothermal hydrogel driven by sunlight includes the following steps:

[0074] (1) Preparation of photothermal material: Dissolve 20 g of sodium lignosulfonate (supplier Macklin) and 4 g of ferric chloride hexahydrate (supplier Macklin) in 180 ml of deionized water, mix well for 2 h at a reaction temperature of 20 °C to obtain an aqueous solution of iron ion-doped lignin photothermal material with high photothermal conversion efficiency (denoted as LS-Fe).

[0075] (2) Preparation of polyvinyl alcohol solution: Thoroughly mix 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water, and stir to dissolve at 90 °C for 6 h to obtain an aqueous solution of polyvinyl alcohol.

[0076] (3) Preparation of hydrogel prepolymer solution: Take 50 g of the solution of lignin photothermal material obtained in step (1) and add it to 100 g of the polyvinyl alcohol solution in step (2). In the finally obtained mixed solution, the mass concentration of polyvinyl alcohol is 10%, and the mass concentration of iron ion-doped lignin is 3.3%. Finally, stir at 80 °C for 6 h to obtain the prepolymer solution.

[0077] (4) Preparation of the photo-thermal hydrogel: Adjust the pH value of the mixed solution obtained in step (3) to 5 using hydrochloric acid, add 0.5 ml of glutaraldehyde (50%) aqueous solution and mix well. Then pour the hydrogel prepolymer solution into a mold (a cylindrical mold with a diameter of 5 cm and a height of 1 cm), and initiate the cross-linking reaction in an oven at 60 °C for 24 h to obtain the photo-thermal hydrogel.

[0078] Comparative Example 1

[0079] A preparation method of a sunlight-driven lignin-based photo-thermal hydrogel, comprising the following steps:

[0080] (1) Preparation of the photo-thermal material: Dissolve 20 g of sodium lignosulfonate (supplier Macklin) in 180 ml of deionized water, mix well for 2 h, and the reaction temperature is 20 °C to obtain an aqueous solution of the pure lignin photo-thermal material (denoted as LS).

[0081] (2) Preparation of the polyvinyl alcohol solution: Thoroughly mix 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water, and stir and dissolve at 90 °C for 6 h to obtain an aqueous solution of polyvinyl alcohol.

[0082] (3) Preparation of the hydrogel prepolymer solution: Take 50 g of the aqueous solution of the pure lignin photo-thermal material obtained in step (1) and add it to 100 g of the aqueous solution of polyvinyl alcohol in step (2). In the finally obtained mixed solution, the mass concentration of polyvinyl alcohol is 10%, and the mass concentration of lignin is 3.3%. Finally, stir at 80 °C for 6 h to obtain the prepolymer solution.

[0083] (4) Preparation of the photo-thermal hydrogel: Adjust the pH value of the mixed solution obtained in step (3) to 5 using hydrochloric acid, add 0.1 ml of glutaraldehyde (50%) aqueous solution and mix well. Then pour the hydrogel prepolymer solution into a mold (a cylindrical mold with a diameter of 5 cm and a height of 1 cm), and initiate the cross-linking reaction in an oven at 60 °C for 24 h to obtain the photo-thermal hydrogel.

[0084] Comparative Example 2

[0085] A preparation method of a sunlight-driven lignin-based photo-thermal hydrogel, comprising the following steps:

[0086] (1) Preparation of the photo-thermal material: Dissolve 20 g of ferric chloride hexahydrate (supplier Macklin) in 180 ml of deionized water, mix well for 2 h, and the reaction temperature is 20 °C to obtain an aqueous solution of iron ions (denoted as Fe).

[0087] (2) Preparation of the polyvinyl alcohol solution: Thoroughly mix 15 g of polyvinyl alcohol solid (1750, Sinopharm Group) and 85 g of deionized water, and stir and dissolve at 90 °C for 6 h to obtain an aqueous solution of polyvinyl alcohol.

[0088] (3) Preparation of hydrogel prepolymer solution: Add 50 g of the aqueous solution of iron ions obtained in step (1) to 100 g of the polyvinyl alcohol solution in step (2). In the finally obtained mixed solution, the mass concentration of polyvinyl alcohol is 10%, and the mass concentration of iron ions is 3.3%. Finally, stir at 80 °C for 6 h to obtain the prepolymer solution.

[0089] (4) Preparation of photothermal hydrogel: Adjust the pH value of the mixed solution obtained in step (3) to 5 using hydrochloric acid, add 0.1 ml of aqueous glutaraldehyde (50%) solution and mix evenly. Then pour the hydrogel prepolymer solution into a mold (a cylindrical mold with a diameter of 5 cm and a height of 1 cm), and initiate the cross-linking reaction in an oven at 60 °C for 24 h to obtain the photothermal hydrogel.

[0090] Performance test of Example 7

[0091] I. Photoresponse performance test

[0092] The photoresponse performance of the aqueous solution of the photothermal material obtained in step (1) of Example 1, the aqueous solution of the pure lignin photothermal material obtained in step (1) of Comparative Example 1, and the aqueous solution of iron ions obtained in step (1) of Comparative Example 2 was tested by wavelength scanning at a speed of 200 nm / min on an ultraviolet-visible spectrophotometer (200 - 2500 nm). The results are as Figure 1 .

[0093] From Figure 1 the transmittance of different photothermal materials, it can be seen that the transmittance of the iron ion-doped lignin prepared in the present invention is lower than 0.5%, showing a wider light absorption range compared to the original lignin, indicating that the doping of metal ions can greatly improve the light absorption performance of lignin.

[0094] II. Photothermal performance test

[0095] The photothermal materials (photothermal hydrogels) prepared in Example 1, Comparative Example 1, and Comparative Example 2 were dried to obtain powders (corresponding to Figure 2 LS-Fe powder, LS powder, and FeCl 3 .6H 2 O respectively). The photothermal performance was tested by heating different photothermal materials with the same mass (10 g) under the same light intensity (1 sun, 1 KW / m 2 ), and using an infrared camera to test the temperature difference to illustrate the thermal conversion performance of sunlight. The results are as Figure 2 shown. The temperature of the lignin powder stabilizes at about 45 °C under light irradiation, while the temperature of the LS-Fe powder is as high as 70 °C and continues to rise, indicating that the obtained photothermal material has excellent photothermal conversion performance.

[0096] III. Bandgap test

[0097] The hydrogels prepared in Example 1 and Comparative Example 1 were subjected to V-XPS and Mott-Schottky tests to calculate the material energy levels and band gaps. The VB-XPS test (valence band spectrum) of the hydrogel was carried out using X-ray photoelectron spectroscopy (XPS, Kratos, Axis Ultra DLD, UK), and the Mott-Schottky curves (frequencies 500 / 800 / 1000 Hz) of the hydrogel were tested using an electrochemical workstation (model CHI660E). The obtained results are as Figure 3 shown, Figure 3 a and Figure 3 b are the Mott-Schottky curves of Comparative Example 1 and Example 1, respectively, and the corresponding measured energy levels are -0.63 eV and -0.56 eV. Figure 3 c is the test result of VB-XPS, and the energy levels corresponding to LS and LS-Fe are 2.61 eV and 2.39 eV, respectively. The test results of the energy level differences are summarized as Figure 3 d. Compared with LS, LS-Fe has a smaller band gap, indicating that the doping of iron ions reduces the band gap (energy level difference) of the composite photothermal material, resulting in easier excitation of photoelectrons, enabling LS-Fe to absorb visible light and infrared light with lower energy, and ultimately leading to an improvement in photothermal performance.

[0098] IV. Solar interfacial evaporation test

[0099] For the solar interfacial evaporation test, the photothermal hydrogels obtained in Examples 1-6 and Comparative Examples 1-2 were placed on the evaporation test platform, as Figure 4 and 5 shown. The evaporation device includes a solar simulator 1, an evaporator 2, and a data acquisition system. The data acquisition system includes an electronic balance 3, an infrared camera 4, and a data recording computer 5, and the electronic balance 3 and the infrared camera 4 are connected to the data recording computer 5. From top to bottom, the evaporator 2 is successively a photothermal hydrogel 6, a water delivery layer 8, a thermal insulation foam layer 7, and simulated seawater 9. The photothermal hydrogel is the photothermal hydrogel prepared in Example 1 (a cylindrical shape with a diameter of 5 cm and a thickness of 1 cm). The water delivery layer 8 is a cellulose cotton cloth with a diameter of 8 cm and a thickness of 0.1 cm. The thermal insulation foam layer 7 is a polystyrene foam, a cylindrical shape with a diameter of 5 cm and a thickness of 2 cm. Usually, 200 ml of simulated seawater 9 (preparing sodium chloride aqueous solutions with concentrations of 0, 3.5%, 5%, and 10% as simulated seawater) is placed in a beaker, then the polystyrene foam wrapped with cellulose cotton cloth is floated on the seawater, and finally the prepared photothermal hydrogel 6 is placed above the cellulose cotton cloth to prepare an evaporator. The power density of the solar simulator 1 is 1 KW / m 2When testing the evaporation rate, turn on the power of the solar simulator, calibrate the light intensity on the surface of the evaporator using a light power density meter, then place the evaporator on the on-line electronic balance 3 to record the mass data of seawater through a computer, and at the same time use an infrared camera 4 to completely record the temperature of the sample. As Figure 6 shown, the mass change data of simulated seawater with different concentrations are presented. It can be seen that the change in the concentration of simulated seawater has a relatively small impact on the evaporation rate.

[0100] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods. Without departing from the core technology of the present invention, improvements and refinements can also be made, and these improvements and refinements shall also fall within the scope of patent protection of the present invention and are all included within the protection scope of the present invention.

Claims

1. A method for preparing a sunlight-driven lignin-based photothermal water gel, characterized in that: The steps include: (1) Preparation of photothermal material: dissolving lignin and an iron compound in a mass ratio of 10:1-1:5 in deionized water to obtain an aqueous solution of lignin photothermal material doped with iron ions; (2) Preparation of polyvinyl alcohol solution: dissolving polyvinyl alcohol in deionized water to obtain a polyvinyl alcohol aqueous solution; (3) Preparation of hydrogel prepolymer solution: adding the aqueous solution of the iron ion-doped lignin photothermal material obtained in step (1) to the aqueous solution of polyvinyl alcohol obtained in step (2), and mixing them evenly to obtain a hydrogel prepolymer solution; wherein the mass concentration of the polyvinyl alcohol in the hydrogel prepolymer solution is 5%-10%, and the mass concentration of the iron ion-doped lignin is 0.1%-10%; (4) Preparation of photothermal water gel: The pH value of the hydrogel prepolymer obtained in step (3) is adjusted to 1-6 using an acid, and mixed evenly with a glutaraldehyde solution, and a cross-linking reaction is induced in an oven to obtain a photothermal water gel.

2. The preparation method according to claim 1, characterized in that: In step (1), the lignin includes at least one of lignin sulfonate, alkali lignin and demethylated lignin; and the iron compound includes at least one of ferric chloride or its hydrate, ferric sulfate and ferrous sulfate.

3. The preparation method according to claim 1, characterized in that: In step (1), the mass concentration of lignin in deionized water is 0.1%-15%; the mixing time of lignin and iron compound is 1-6 hours, and the temperature is 10-80°C.

4. The preparation method according to claim 1, characterized in that: In step (2), the mass concentration of polyvinyl alcohol in the polyvinyl alcohol aqueous solution is 5%-15%; the polyvinyl alcohol solid and deionized water are fully mixed, and stirred and dissolved at 80-95° C. for 1-6 hours to obtain the polyvinyl alcohol aqueous solution.

5. The preparation method according to claim 1, characterized in that: In step (3), the conditions for uniform mixing are: stirring temperature 20-80° C., and stirring time 0.5-6 hours.

6. The preparation method according to claim 1, characterized in that: In step (4), the glutaraldehyde solution is a glutaraldehyde aqueous solution with a volume concentration of 50%; the amount of the glutaraldehyde solution added is 1%-5% of the mass of the polyvinyl alcohol; the cross-linking temperature is 20-90°C, and the cross-linking time is 1-24h.

7. The sunlight-driven lignin-based photothermal water gel prepared by the preparation method according to any one of claims 1 to 6.

8. A sunlight-driven lignin-based interfacial evaporator, characterized in that: The interfacial photothermal evaporator comprises an evaporator body, which comprises a photothermal water gel, a water transport layer and a thermal insulation foam layer arranged in sequence from top to bottom. The photothermal water gel is the sunlight-driven lignin-based photothermal water gel as described in claim 7.

9. The solar-driven lignin-based interfacial evaporator according to claim 8, characterized in that: The water transport layer is cellulose cotton cloth or dust-free paper, and the heat insulation foam layer is polystyrene or polyurethane foam; Or the interfacial photothermal evaporator further includes a solar simulator and a data collection system.

10. Use of the sunlight-driven lignin-based interfacial evaporator according to claim 8 or 9 in seawater desalination.

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